Semiconductor devices are designed to achieve the highest integration levels possible. Higher levels of integration realize a cost savings because more features can be incorporated into a given device area, the integrated circuit or other semiconductor devices can be formed on smaller and smaller chips and a greater number of chips can be simultaneously manufactured on a given substrate.
Semiconductor devices are typically designed to include repeating cell structures. Each cell structure includes interconnected active devices and is coupled to other similar and different cells, and to other features. The cells may be NAND cells, NOR cells, stacked NMOS cells, stacked PMOS cells or any of various other cell structures used in semiconductor manufacturing. The cell structure arrangement is favored for design efficiency, i.e., once a cell is designed, it can be selected and used multiple times in the layout of the integrated circuit or other semiconductor device.
The placement of the cells in a device is critical. The layout of the features within the cells is also critical because it is desirable to form as many active devices as possible in a given cell. It is also desirable to design the cells to be as small as possible and to route as many signal and power lines as possible, through the cells for coupling to other cells and to other features. There are minimum spacing design rules that must be followed for the metal tracks such as the signal and power line tracks that extend through the cells. These minimum spacing design rules limit the number of metal tracks that can extend through the cells. As such, when more signal tracks are needed due to the complexity of the cell or the semiconductor device, they cannot simply be added. Rather, signal tracks must be added at the expense of power tracks, i.e. less space is available for power tracks and this limits device performance.
It would therefore be desirable to increase the number of metal tracks that may be accommodated within a cell and to generally increase integration levels and complexities of such repetitive cells.